The research on this project will focus on factors influencing the metabolism of the branched-chain amino acids -- leucine, isoleucine and valine -- in the rat. Studies are currently being done on oxidation of valine by the isolated, perfused rat hindquarter as a model for metabolism in muscle. This preparation converts valine to alpha-ketoisovaleric acid rapidly but the alpha-ketoacid is released from muscle into the perfusion medium. This acid is also found in blood plasma of rats. The projected studies will be directed toward examining the effects of nutritional modifications on valine transamination and oxidation of the valine carbon skeleton in both the perfused hindquarter and the intact rat. In particular, effects of varying the protein intake of the rat and effects of altering the leucine and isoleucine concentrations in the perfusion medium and in the diet will be examined. In parallel with these studies, in vitro experiments will be performed with purified aminotransferase and dehydrogenase preparations to investigate the effects of competition among the branched-chain amino and alpha-ketoacids on the proportions of products formed in these reactions.